The present invention disclosed herein relates to a photon detector, and more particularly, to a single photon detector and a photon number resolving detector, which use an avalanche photo diode.
With the advance of quantum encryption communication and information communication technologies, technology of detecting a photon is becoming increasingly more important. Particularly, an InGaAs/InP type of avalanche photo diode is mostly used in single photon detectors that are used in a telecommunication band such as 1.3 μm to 1.5 μm and detect an optical signal that is weak in intensity as in a single photon level. InGaAs/InP type of avalanche photo diodes are mostly used in a gated Geiger mode.
When an avalanche photo diode operates in a gated Geiger mode, some of charge carriers generated in an avalanche arising operation are not immediately vanished. Charge carriers that are not completely vanished are left inside an avalanche photo diode, and when a next gate signal is applied to the avalanche photo diode, the left charge carriers lead to an avalanche. Such an effect is called an after-pulsing effect, which is one of important causes that raise an error in detecting a photon.
As a method of reducing errors due to the after-pulsing effect in detecting a photon, there is a method that sets a dead time sufficient to remove the charge carriers that are left inside an avalanche photo diode without being vanished after an avalanche arises. That is, a dead time is set in which a gate signal is not applied to an avalanche photo diode for a predetermined time after an avalanche arises.
However, since typical photon detectors detect a relatively large avalanche, there are relatively many charge carriers that are left without being vanished. Therefore, a dead time sufficient to remove the left charge carriers is required to be set long. As a result, such an after-pulsing effect and dead time are important factors that determine a gating frequency of a gate signal and the limit of a photon count rate, and thus, typical single photon detectors operate at a gate frequency of about 10 MHz or less.